In the past decade, Nano-ElectroMechanical Systems (NEMS) have been gaining increasing attention for their superb ability to detect mass and force on the atomic scale.1-3 The development of sensors based on large-scale integrated NEMS is likely to open up a broad spectrum of applications in science and technology and revolutionize a range of fields from mass spectrometry4 to biomedical diagnostics.5 In the present specification, a novel transduction principle in a silicon nanowire electromechanical resonator is shown, which exploits the depletion charge modulation in the self-aligned, junctionless Field Effect Transistor (FET) body as an intrinsic displacement transducer. A mechanical resonance at the very high frequency of 226 MHz is detected in the drain current of the highly doped silicon wire with a cross section of 28×35 nm2. The signal gain and tunability inherent to this device can be harnessed to build nano-oscillators,6 which can be integrated to high densities in silicon-on-insulator (SOI) complementary metal-oxide semiconductor (CMOS) conventional technology and therefore offer unique opportunities for NEMS-based sensor and signal processing systems hybridized with CMOS circuitry on a single chip.
All existing NEMS are based on a mechanical transducer, i.e., an input and output element that converts a form of energy into mechanical motion, and vice versa. Numerous mechanisms have been introduced, including electrostatic,7 electromagnetic,8 piezoelectric9 or optical10 schemes, among others, which can be combined for mechanical actuation and motion detection. In the last decade, mechanical resonators have undergone a continuous reduction in dimensions, reaching molecular levels in the form of carbon nanotubes or graphene11-12 One reason for this development is that NEMS, because of their inherent properties as mechanical sensors, tremendously benefit from size reduction.13 The detection of mass and force in the attogram (10−18 g)— and attonewton (10−18N)— range, respectively, has been repeatedly demonstrated1, 2, 14 To unfold the full potential of these resonators, fabricating and controlling a very large ensemble of NEMS that comprise tens of thousands of resonators, is necessary. Large area technologies that enable the parallel processing of mass information have a great impact on the development in several fields,15 such as system biology, where the parallel operation of millions of FET-based sensors recently enabled non-optical genome sequencing on-chip.16 In terms of NEMS, these requirements severely limit the choice of material and of the type of mechanical transducer. Silicon technology remains therefore a promising avenue to follow for NEMS-based systems targeting a high level of integration and complexity. The piezoresistive effect in silicon has been exploited in nanowire resonators operating at very high operating frequencies. However, transduction schemes employed therein required a detection circuitry involving frequency generation at twice the resonator's natural frequency,17 or a complex modal shape design of so-called crossbar cantilevers.18 